Please, please, please, do NOT use W3Schools. Their content is outdated and promotes bad code. See why here: http://w3fools.com/
There are many aspects of web development that you can get into. Regardless, you're probably going to have to learn one or more scripting languages like JavaScript if you're going to do client side programming. You'll also have to understand concepts like HTML, CSS, HTTP, DOM, AJAX, etc.
If you also want to program the server-side portion of a website, you're looking at even more work nearing computer science than web design. You'll have to understand how relational database systems work, how to manipulate them, how to protect it against hackers ( all the "hax0rs" out there on the news are a testament to the problem), and how to streamline an application. You'll also be looking at software design patterns, mainly MVC (Model View Controller). As for languages, server-side programming could be done on a range of programming languages ( including C++!). The traditional languages are of course PHP, Python, Perl, Ruby, and Python if you choose to work with the .NET platform, there is of course ASP.NET.
You use these languages to process data ( perhaps from a database via SQL queries) and send it to the client ( the user's computer) where it is further processed and displayed to the user, using JavaScript.
It's a lot to take in, but like everything in life, you learn it one step at a time. For now I suggest you get a head start on HTML and CSS, with readings about the Document Object Model (DOM):
Resources:
http://eloquentjavascript.net/contents.html
http://www.html5rocks.com/en/
and my favorite:
https://developer.mozilla.org/en-US/